A pet pen can be described as an enclosure for keeping a pet. An example of a pet pen in which a plurality of panel bodies are put together to form an enclosure is disclosed in Japanese Publication No. 2006-271215.
In addition, although not a pet pen, Japanese Patent No. 3098127 discloses a pet cage in which the housing space can be changed in accordance with the type and size of the pet.
The pet cage of Japanese Patent No. 3098127 has a bottom frame that is positioned at the bottom of the housing space. One or more of a middle frame are positioned in the middle of the housing space, and a top frame is provided at the top of the housing space. A support column is provided so as to be removable from the bottom frame, the middle frame, and the top frame. In the case where the middle frame is arranged between the bottom frame and the top frame, linear plates, which are installed so as to be removable between the middle frame and bottom frame or between the middle frame and the top frame and partition the housing space area, are combined with the frames and have one level or multiple levels.